Many circuits, networks, electrical devices and data handling systems are operated in configurations and environments where external factors can impair their performance, cause failure or even result in permanent damage. Among the most common of these factors are over-voltage and over-current transients. Protection against these is important and has been addressed in the prior art in a number of ways, depending on the specific electronics and their application.
Fuses that employ thermal or magnetic elements are one common protection measure. For example, some circuits employ relays in their systems to cause protective blocking in either direction. Exemplary prior art protection circuits that use relays, including circuits with MOSFETs, include U.S. Pat. Nos. 4,453,191; 4,484,245; 5,536,980; 5,926,354; 6,373,670; 6,759,835 and 6,891,705.
Protection circuits are further specialized depending on conditions and application. For example, in the case of protecting batteries or rechargeable elements from overcharging and over-discharging one can refer to circuit solutions described in U.S. Pat. Nos. 5,789,900; 6,313,610; 6,331,763; 6,518,731; 6,914,416; 6,948,078; 6,958,591 and U.S. Published Application 2001/0021092. Still other protection circuits, e.g., ones associated with power converters for IC circuits and devices that need to control device parameters and electric parameters simultaneously also use these elements. Examples can be found in U.S. Pat. Nos. 5,929,665; 6,768,623; 6,855,988; 6,861,828.
When providing protection for very sensitive circuits, such as those encountered in telecommunications the performance parameters of the fuses and protection circuits are frequently insufficient. A prior art solution which satisfies a number of the constraints and is embodied in a transient blocking unit (TBU) is taught in international applications PCT/AU94/00358; PCT/AU04/00117; PCT/AU03/00175; PCT/AU03/00848 as well as U.S. Pat. Nos. 4,533,970; 5,742,463 and related literature cited in these references.
One significant limitation of the TBU is that it does not have the capability of resetting itself in response to short-lived transients, such as those caused by lightning, or staying blocked in response to persisting transients or permanent over-voltage or over-current conditions. In fact, the TBU has no provisions for distinguishing between short-lived and persisting transients. It would thus be an advance to provide a TBU with a reset function that recognizes the various types of transients and controls the TBU accordingly.